Bonded nonwoven backing material having perforate selvage and carpet made therefrom



Dec. 26, 1967 s. SANDS 3,369,421

BONDED NONWOVEN BACKING MATERIAL HAVING PERFORATE SELVAGE AND CARPET MADE THEREFROM Filed April 25, 1965 INVENTOR SEYMOUR SANDS ATTORNEY United States Patent 3,360,421 BONDED NONWOVEN BACKING MATERIAL HAVING PERFORATE SELVAGE AND CAR- PET MADE THEREFROM Seymour Sands, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Apr. 23, 1965, Ser. No. 450,487 11 Claims. (Cl. 161-63) This application is a continuation-impart of Ser. No. 279,579 filed May 10, 1963.

This invention relates to nonwoven fabrics having improved structural stability. More particularly, it concerns such nonwoven fabrics which are highly suitable for use as carpet backing material and tufted carpets produced therefrom.

Nonwoven fabrics have been produced in the past by a variety of processes. In general, the fibers of the web are bonded by some means such as by the application of heat or a solvent to fuse or coalesce the fibers or by the application of an external binder or adhesive. For many uses, the extent of bonding must be such that adequate strength is provided without producing deleterious effects on other properties. One such use is in the production of nonwoven fabrics for use as backing materials for tufted rugs. This use requires that the nonwoven fabric must have sufiicient strength to undergo continuous process ing such as tufting, dyeing, drying, latexing and other operations. In the area to be tufted, a certain degree of fiber mobility must be retained so that, during the tufting operation, the strength of the nonwoven fabric is not destroyed by rupture of the fibers by the tufting needs. The desired mobility can be attained in a bonded, continuous filament, nonwoven fabric which is specially designed and treated so that during tufting, bonds break rather than filaments. Since the breaking of bonds in the tufted area is compensated for by the reinforcing action of the tufting yarns in that area, adequate strength for further processing is maintained. However, such a nonwoven fabric often is lacking in adequate delamination resistance to undergo repeated flexing, abrasion, and similar frictional working such as occur before, during and after tufting. The problem of delamination is severe in the areas which are not tufted, that is, along the edges by which the backing material is held and supported during processing. Thus, during processing, individual fibers and groups of fibers become pulled away from the body of the fabric thereby creating a highly fuzzed surface which renders the intermediate product unsatisfactorily for further processing.

The present invention provides a nonwoven fabric having improved delamination resistance.

The present invention further provides a nonwoven carpet backing material having sufficient strength to be processed and suflicient delamination resistance to prevent fuzzing during processing.

More specifically the present invention provides a nonwoven carpet backing With a selvage having a high degree of delamination resistance. It further provides a tufted product from such a nonwoven fabric. These and 3,360,421 Patented Dec. 26, 1967 other advantages of the invention will become apparent from the following disclosure and claims.

The novel products of this invention are non-woven fibrous sheets comprised substantially of fibers of a thermoplastic polymer, the sheet having a predetermined number of perforations per unit area present in at least a portion of the sheet, the fibers around the walls of each perforation being fused together throughout the depth of the perforation.

More particularly, the products of the present invention are nonwoven sheets suitable for use as carpet backings and comprising continuous filaments disposed in random fashion and bonded to one another at a multi-, plicity of bond points throughout the sheet, the sheet further having, atleast along te edges thereof, between about 20 and perforations per square inch, the filaments in the walls of each perforation being fused together throughout the depth of the perforation. The perforations are preferably located within a 3-inch strip along edges of the sheet to provide a delamination-resistant selvage for the sheet.

According to a more specific embodiment the products of this invention are tufted carpets having a primary backing which is a nonwoven sheet comprising randomly disposed, continuous filaments, the sheet having perforations along the edges thereof at a density of between about 20 and 80 perforations per square inch, the filaments in the walls of each perforation being fused together throughout the depth of the perforation.

Nonwoven sheets which are suitable for use as carpet backings can be prepared by forming a sheet of randomly disposed, continuous filaments, bonding the sheet and treating it with a lubricant under specified conditions so as to produce a sheet having suificient bond sites to provide adequate strength to the sheet and sufficient fiber mobility to prevent loss of this strength and excessive damage to the sheet during tufting. The conditions neces sary to obtain such tuftable nonwoven sheets will be discussed in more detail hereinafter.

The desired perforations may be produced in the nonwoven sheet by contacting the sheet at the desired number of sites with means having a temperature sufficient to at least partially soften or melt the thermoplastic fibers while simultaneously perforating the sheet at the site. Preferably, an electric or spark-discharge treatment is used to simultaneously perforate the sheet and fuse the fibers at the perforations edge, Suitable means for spark-perforating the sheets are described in US. Patents 2,141,869 and 2,372,508 among others. Alternatively, a plurality of spaced-apart heated needles or needle-like elements may be inserted into the sheet at the desired locations to simultaneously perforate the sheet and fuse the fibers at the wall of each perforation.

The number of perforations provided in the sheet is highly important if one is to obtain a nonwoven fabric having both adequate strength and delamination resistance. Thus, if the perforations are too numerous, sheet strength is decreased and eventually destroyed despite any reinforcement which the fiber-fusion may provide If the perforations are too few, delamination resistance is insufiicient to prevent fuzzing and separation of filaments from the sheet surface.

In the manufacture of carpets, using a nonwoven sheet as a primary backing, delamination is often evidenced by the development of a fuzz/ed surface during the processing steps subsequent to the tufting operation and, in particular, upon subsequent passage through the dye beck. This delamination and the accompanying weakening of the sheet make it impossible to continue to process the backing through the remaining operations of tentering, latexing, etc. In practice, the presence of the tuft yarn helps the tufted area of the fabric by serving as a reinforcement. Thus, for use as a carpet backing it is only necessary that the nonwoven fabric have a selvage (as is commonly provided in woven goods) which is delamination-resistant. Further, it is desired to provide this by a means which is convenient, adaptable for use with commercial processing equipment, and sufficiently flexible to provide for varying the area or extent of the treatment.

It has been found that nonwoven sheets can be provided with improved delamination resistance in a convenient, rapid, and efficient manner by hot-perforating the sheet in the desired area, such as by hot-needling or by spark-discharge treatment, whereby numerous minute perforations having fused-fiber walls are provided in the sheet. The entire sheet or only a portion thereof may be continuously treated, as desired. The process is versatile in that suitable hot-perforating means may be incorporated with existing fabric processing equipment to provide for the treatment. Thus, if it is desired to provide a delamination-resistant selvage for a nonwoven sheet to be used as a rug backing material, a heated needling roll or a spark-discharge device may be added to the commercial tufting equipment to hot-perforate only the edge of the nonwoven sheet as the latter is being processed, for example, as it is being forwarded toward the tufting zone.

The degree of treatment may be characterized by the number of perforations per unit area of sheet, the size of the holes, and their distribution throughout the sheet.

The number of perforations should range between about 20 and 80 per sq. in. If fewer than about 20 holes are provided, the fiber-fusion sites are too few to confer adequate delamination resistance. Thus, if the nonwoven sheet is used as the primary backing in the production of a tufted carpet, the edges of the sheet will be badly delaminated by the time the sheet passes through the dye beck rendering the sheet too weak at its edges to be supported by the pins of the tentering device. If more than about 80 fused-edge holes per sq. in. are provided,

tensile strength of the sheet is reduced to an unacceptable level by reason of the perforations. Thus, the nonwoven backing sheet will rupture along the perforations as the tufted sheet is passed through the tentering step. The tentering step is a commonly employed finishing step in the commercial carpet manufacturing processes. In this step, the carpet is held along its edges and is pulled taut so as to correct any dimensional irregularities which may have resulted, for example, from passage of the tufted backing through the dye beck.

The perforations, which extend vertically through the sheet, should be fairly evenly distributed throughout the edge area of the sheet. Preferably they should not be clustered in one portion of the treated area and absent in another, although some latitude may be permitted in this location while attaining the present objectives. Thus, distances of 4 inch between perforated areas of about one inch in length along the edge of the sheet may be present without severe diminution of the beneficial results of the invention. It is not, however, necessary for the perforations to be aligned or distributed in an orderly pattern. However, as the number of perforations increase (toward the upper limit of 80) it is generally preferred that they be dispersed more or less randomly throughout the treated area since this reduces the tendency for tearing along any given line of perforations.

The size and spacing of the perforations are, of course, dependent on the frequency and distribution of the perforations. Suitably, the holes may range in diameter from approximately 0.2 mm. to as much as about 3 mm., the average hole diameter being about 0.5 mm. or greater. The edge-to-edge distance between any hole and its nearest neighbor may suitably range between about 0.2 and 16 mm. and average between about 2 and 7 mm.

In the preferred practice of this invention, a nonwoven sheet suitable for use as a carpet backing material is prepared in the following manner:

First, there is formed a nonwoven web comprising continuous synthetic organic filaments disposed in a random, nonparallel fashion. The web is preferably substantially free from filament aggregates which factor contributes significantly to the improved covering power and high strength. Filaments having a denier per filament of between about 3 and 15 (0.3 to 1.7 tex) are employed. The filaments may be crimped or straight and may be round in cross-section or of different shapes such as trilobal. Filaments of polymers selected from the group consisting of isotactic polypropylene, linear polyethylene, crystalline copolymers of at least propylene or ethylene with up to 25% of other copolymerizable monomers and mixtures of isotactic polypropylene or linear polyethylene with up to 25% of other polymers, preferably hydrocarbon (e.g., atactic polypropylene, branched polyethylene, polyisobutylene) are useful for this invention. The process of British Patent 932,482 is especially suitable for the formation of the nonwoven webs used in the preparation of the nonwoven sheets of this invention.

Second, the nonwoven web is exposed to bonding conditions so as to produce a bonded sheet having a multiplicity of bonds of such strength that, during tufting of the sheet after lubrication as described hereinbelow, filament breakage is minimized. It is believed that such bonded sheets permit filaments to be displaced and bonds to break as the tufting needles penetrate the sheet. Thus, for the most part, the filaments remain intact and accordingly, the sheet retains sufiicient strength for subsequent processing steps.

As a third and essential step, there is applied to the bonded sheet a polar fabric lubricant such as methyl hydrogen polysiloxane, dimethyl polysiloxane, 2-ethylhexyl silicate, Z-ethylhexyl sebacate, dioctyl sebacate, acetyl 2-ethylhexyl citrate, refined coconut oil, potassium oleate, potassium n-octyl phosphates, diethanolamine salts of C -C alkyl hydrogen phosphates and mixed n-octyl fl-hydroxy ethyl esters of phosphoric acid, in an amount such that at least 0.3% and up to 5% lubricant based on the nonwoven sheet is present on the surface of the filaments at the time of tufting.

The thus obtained, tuftable nonwoven sheet is then hot-perforated in accordance with the present invention to provide between about 20 to perforations per sq. in. along the edges of the sheet that will be subjected to tentering to provide a delamination-resistant selvage. The perforations may start at the edge of the sheet or up to about A" from the edge and may extend inwardly to the area to be tufted or to within about A of the area to be tufted.

The nonwoven sheet so produced may then be tufted with known carpet yarns, preferably at a stitch spacing of between 4 and 15 stitches per inch (1.6 to 5.9 per cm.), using tufting needles having a diameter of from 0.100 to 0.180 inch (0.254 to 0.457 cm.). After passage through the tufting zone and using commercial equipment, the tufted sheet may be passed through the dye beck and then dried, latexed, and stabilized in a pin tenter or like tentering device. If desired, a secondary backing in the form of a nonwoven sheet of continuous strands of polypropylene or other suitable sheet may also be applied. Usually, a latex adhesive is used to anchor the tufts in the backing and optionally to adhere the primary and secondary backing materials to one another.

BONDING METHODS FOR MAKING TUFTABLE SHEETS As stated above, bonded sheets of continuous filaments are used as the initial sheets for primary carpet ba-ckings in accordance with the present invention. The sheets can be between 0.005 and 0.030 inch (0.013 to 0.076 cm.) thick and are preferably 0.010 to 0.025 inch (0.025 to 0.064 cm.) thick.

Embodiment one In one embodiment the bonds in such sheets derive from the fiber elements themselves and occur at crossover points between fibers. The filaments in the bonded sheet possess a birefringence that is at least 40% of the calculated maximum birefringence possible for them. For such self-bonded sheets the required bond structure in the sheets is characterized by an edge bond count (EEC) of between 30 and 80 bonds per hundred filaments. Determination of edge bond count is discussed in more detailed hereinafter.

The preferred method for making this embodiment of the primary backings is by exposing throughout its three dimensions, a nonwoven web comprising randomly disposed continuous, isotactic polypropylene filaments, the web being substantially free from filament aggregates and the filaments having a birefringence of between about 0.016 and 0.04 and a crystallinity index of at least 40%, to saturated steam at a temperature in the range from about 45 C. below up to the crystalline melting point of the polymer while restraining the web with a force suflicient to prevent filament shrinkage of more than 20%. Temperature variation throughout the web is maintained within a 0.5 C. range. The heat-up rate and the selected exposure temperature must be sufficient to self-bond the filaments at a plurality of spaced intersection points to provide a sheet having a strip tensile (ASTMD39 using a specimen 2.0 x 2.5 cm.) of at least 3 lb./in.//oz./yd. (16 g./cm.//g./m. while preventing a drop in filament birefringence of greater than 50%. Also the bonding temperature must be below that which would produce an edge bond count above 80 or a birefringence lower than 40% of the calculated maximum birefringence of the filament. By this method, no loss of fiber identity occurs.

Maximum birefringence is determined in accordance with H. M. Morgans Correlation of Molecular Orientation Measurements in Fibers by Optical Birefringence and Pulse Velocity Methods, Textile Research Journal, 866, October 1962. The maximum birefringence for filaments of isotactic polypropylene is 0.04 and for linear polyethylene is 0.06.

In addition to the filaments heretobe-fore described, up to 25% by weight of the total web may comprise other filaments which will not self-bond under the bonding conditions employed. These other filaments may be termed inert filaments and may be made of glass, metal or other inorganic or organic substances. There may also be present small amounts of adjuvants such as fillers, delusterants, pigments, coloring materials, stabilizers and the like. For example, ultraviolet light stabilizers may be incorporated into the polymer before spinning into filaments.

The range of temperature for self-bonding filaments is relatively narrow and lies between 45 C. below the crystalline melting point of the polymer up to the crystalline melting point. The crystalline melting point can be determined by the method outlined in Preparative Methods of Polymer Chemistry by W. R. Sorensen and T. W. Campbell, Interscience Publishers, Inc., 1961, pp. 44-47. In applying the procedure to fibers it is necessary to immobilize the fibers on the slide by securing their ends with a suitable heat-resistant adhesive or tape. The crystalline melting point may not be exceeded, and in some instances even lower temperatures may be too high for the process because of too rapid a heat-up rate.

By self-bonded is meant that the highly crystalline and oriented filaments are fused to each other at crossover or intersection points. No foreign material is present to effect bonding. Filamentand web-geometry of the bonded sheet are substantially the same as those of the unbonded web except for the bonds. In some cases, fiattening of filaments occurs because of the restraining forces employed.

Microscopic studies show that the major cross-sectional dimension of each filament at the bond site is less than twice that of the unbonded filament segments adjacent the bond sites. It is also noted that the bonds are weaker than the filaments as evidenced by the fact that exertion of a force tending to disrupt the sheet, as in tufting, will fracture bonds before breaking filaments.

The bonded webs will exhibit an edge bond count (E-BC) of between 30 and bonds per hundred filaments. Lower levels of bonding result in sheet materials having relatively low tensile strength. Exceeding an EBC of 80 results in excessive filament breakage during tufting. Sheet tear properties are also deleteriously affected at high BBC. Low tear strength is also obtained where filament birefringence is less than about 40% of maximum birefringence. By achieving high filament orientation along with the indicated degree of bonding, the unique result of both high tear and tensile strength is obtained.

The bonded sheet materials will contain self-bonds which are distributed throughout the textile product both randomly and uniformly. However, it should be realized that certain modifications may be made either during the bonding process or thereafter to modify this distribution to some extent.

The method employed for determining the average edge bond count (EBC) of bonded samples is described below. Since the presence of lubricant might interfere with the measurement it is preferred that the determination be made prior to addition of lubricant or after its removal from the web.

The number of bonds per filaments, as counted on the edge face of a bonded web is used as a measure of the amount of self-bonding. This count is based on the probability that the appearance of a bond at an edge face is dependent upon (1) the number of bonds, (2) the size of the bond, and (3) the distribution of these bonds.

The edge bond count measurements are made on samples taken from a representative 6-inch (15 cm.) square test piece of bonded sheet. Four samples are taken from the test piece, one from near each of the four corners in such a fashion that the cross sections to be count ed later will come from edges parallel to the four edges of test piece. These samples are fastened in a frame and embedded in an epoxy resin which is then polymerized. The embedded specimens are trimmed so that at least a 0.25 in. (0.64 cm.) cross section of the sheet is exposed for microtoming. These samples are microtomed transversely to the face of the sheet at a thickness of about 6 microns, and the resulting sections are deposited in immersion oil on the micrometer stage of a polarizing Projectina No. 4014. This apparatus is a microscope (ditributed by Hudson Automatic Machne and Tool Company, 137-139 Thirty-Eighth Street, Union City, N.J.), which projects a View of the section onto a screen where the filaments and bonds are counted. A 10 eye-piece and a 20X objective lens are used. The polarizer and an R-I red filter are used to improve filament definition. In the projected view, the filaments will appear in various shapes depending on the angle at which they were cut by the microtome. Thus all the variations from a transverse cut perpendicular to the filament axis to a longitudinal cut parallel to the filament axis may be present. Each filament in the projected View is counted once. A bond occurs and is counted whenever there is no complete separation between any two filaments. Thus, while a filament is counted only once, that filament may participate in from to or more bonds depending on the number of other filaments it contacts. For example, if a filament contacts two other filaments, the filament count is 3 and the bond count is 2. If the other two filaments also contact each other, the filament count is 3 and the bond count is 3. At leaest one full 0.25 in. (0.64 cm.) slice is counted and not less than 200 filaments from each embedded sample. The number of bonds per 100 filaments is averaged from the four samples and reported as the average edge bond-count.

A measure of the crystallinity index of the synthetic organic polymeric filaments can be obtained by means of X-ray diffraction techniques.

In order to determine the birefringence of filaments within a bonded sheet structure, a thin layer of the sheet is obtained either by careful delamination or by sectioning with a razor blade. This is necessary since light must pass through the filament being tested without interference from other filaments. The birefringence of round filaments may be determined using a polarizing microscope with a Berek compensator known to the art. Measurements should be made on at least ten filaments and the results averaged.

Embodiment two In another embodiment of bonded nonwoven sheets which can be used in the lubricated products of this invention, the bonds required for adequate filament mobility during the tufting operation are characterized as follows, considering only those bonds which have a strength greater tahn 0.1 gram: (1) the average bond strength CS) is at least 0.9 gram and less than the filament-breaking strength; (2) the distribution of bond strengths is such that the variance ((7-2) is greater than 4 and (3) the number of bonds is such that the product (N 8 of the number of bonds per cubic centimeter (N and the average bond strength is greater than 5x10 g./cm. and this product divided by the filament-breaking strength is less than 9 10 /cm. The filament-breaking strength referred to above is the strength in the bonded nonwoven sheet. Variance, as used herein, has its accepted meaning in statistical analysis and is defined as follows:

r is the variance g is the arithmetic mean of the bond strengths s is the measured value of the individual bond strengths,

and

m is the number of measurements.

It has been found that nonwoven sheets which have the above-defined bond characteristics and which have been properly lubricated, provide tufted carpets with a good combination of grab-tensile strength and dye-beck width loss. By dye-beck width loss is meant the percent of width reduction occurring when the tufted carpet is put under tension in the machine direction during the dyeing operation. These nonwoven sheets differ from the self-bonded sheets used in the first embodiment of this invention in having a broader distribution of bond strengths. This broad distribution permits wide limits on the average bond strengths and bond concentrations to give acceptable products. A narrow distribution product, such as the self-bonded sheets previously described, necessitate very narrow limits on the number of bonds and precise regulation of the bonding conditions to obtain a good product.

The nonwoven sheets of embodiment two are composed of matrix filaments of hydrocarbon polymers of the same types as used in the self-bonded structures. However, instead of depending solely on self-bonds, adhesive bonds,

that is, bonds between two different materials, can also be present and satisfactory sheets are obtained if the bond strength and concentration come within the structural limitations defined above.

A particularly preferred sheet material for use in embodiment two is produced from nonwoven webs of continuous filaments of oriented isotactic polypropylene as the matrix filaments and unoriented or low-oriented isotactic polypropylene filaments as the binder material. By virtue of the lower degree of orientation in the binder filaments, they have a lower softening point than the matrix filaments. By choosing the proper bonding temperature, bonds comprising self-bonds between the matrix filaments, self-bonds between the binder filaments and inter-bonds between the matrix and binder filaments can be produced. Since these can have different bond strengths, the required variance in bond-strength distribution can be readily obtained. It is necessary when practicing this method, however, to operate the bonding step at a sufficiently high temperature to obtain some degree of selfbonding between the matrix filaments. This can be readily obtained since the softening point of the low-oriented binder filaments is usually only about 5-l0 C. below that of the more highly oriented filaments.

The binder filaments can be incorporated into the nonwoven web as separate low-oriented filaments or as low-oriented segments of mixed orientation filaments. Either of these methods can readily be adapted for use in the aforementioned process of British Patent 932,482 for the production of continuous-filament nonwoven sheets. Separate binder and matrix filaments can be produced by using two separate spinning and drawing machines and combining the filaments prior to or during web laydown. They can also be produced by splitting the thread line from the spinneret so that a part bypasses the drawing operation. Another method involves the use of a spinneret with varying capillary geometry which produces filaments with varying responses to the drawing operation. Nonwoven webs of filaments with segments having different levels of orientation can be produced by pulsing the throughput of polymer going to the drawing operation, by pulsing the draw ratio in the draw-ing operation, or by variation of the drawing temperature. This latter method can be carried out by passing the filaments over a fluted feed roll in the drawing step. It has been found that these various techniques produce satisfactory mixed-orientation webs for use in producing the nonwoven sheets of this invention.

The oriented polypropylene matrix filaments in the unbonded nonwoven web will normally have a birefringence in the range of 0.020 to 0.040, while that of the binder filaments will be in the range of from less than 0.01 to about 0.03 and will always be less than that of the matrix filaments.

As indicated above, it is necessary to carry out the bonding of the nonwoven web under such conditions that some degree of self-bonding between the matrix filaments will be obtained. The bonding procedure described previously for self-bonding of nonwoven webs of oriented polypropylene filaments is applicable to the bonding of these nonwoven webs of mixed orientation filaments. Thus the nonwoven web is held under restraint while being exposed to a saturated steam atmosphere at the pressure required to obtain the desired bonding temperature. While regulated bonding conditions are required to obtain the required bond strength, distribution and concentration, the bonding conditions are much less critical and it is easier to produce acceptable product than with the nonwoven webs which are bonded solely by self-bonds between the matrix filaments. While self-bonding of oriented filaments requires temperature regulation within a range of about 0.5 C. and preferably within 01 C., the bonding of mixed-orientation webs can be carried out within a range of about 3 C. and preferably within a range of 1 C. The bonding temperature used with the mixed-orientation webs is also lower, thus it is easier to maintain the desired birefringence in the matrix filaments, which is indicative of good filament tenacity.

A method which can be used to measure the average bond strength of webs prepared in accordance with embodiment two is described below. A sample of the bonded nonwoven sheet (2 in. x 0.125 in.) (5 cm. x 0.32 cm.) is delaminated into as many layers as can be obtained without distortion of the individual strips. The number of layers obtained will vary with the product being tested but will usually be between 3 and 10. The purpose of delaminating and using narrow samples is to obtain layers having a limited but representative number of bonds so that in the subsequent tensile test, individual bond breakage can be followed and the likelihood of multiple bonds breaking simultaneously is minimized. Each of the delaminated layers is pulled apart in an Instron Tensile Tester using a l-in. (2.5 cm.) jaw separation and a strain rate of 0.02 in. (0.05 cm.) per minute. The instrument is calibrated to 40 grams full scale, thus permitting readings down to 0.1 gram. Bonds having strengths less than 0.1 gram are not measured. On the stress-strain curve so obtained, the drops in load, after the maximum stress (F is reached, are attributed to breakage of individual bonds. The magnitudes of these drops, which correspond to individual bond strengths, and their number are determined.

As a delaminated layer is elongated, the resultant stress (F) is distributed over the bonds supporting the stress in the strip. At any section across the layer the stress (F) will be distributed among the bonds supporting stress within that section. The stress potential of such section will be determined by the product of the number of bonds (N supporting the stress and their average strength (S). When the force on the layer exceeds the value of N S for the weakest section of the layer, it will begin to fail at that point, and bonds in that section will begin to break. At higher elongations, the layer is held together by a few fibers and on continued elongation, bonds are broken in sections further back and outside the original section of the bond breakage. This expanding area of bond breakage is not definable and some basis is needed to limit the bond-strength measurement to some small finite section which can be measured. The proper amount of elongation is determined from the maximum stress recorded (F which is equal to N S for the section of the layer which breaks. Accordingly, the layer is elongated until the value of N S and F give the required agreement.

The section of bond breakage is determined by taking photomicrographs of the delaminated layers before and after the bond-breaking test, comparing the same and measuring the area of disruption. This is the area that does not remain intact as seen from a comparison of the before-and-after photomicrographs. The thickness of the original sample can be readily measured by known methods, for example, with an Ames gauge. From the area of bond breakage and the thickness of the original nonwoven sheet sample, the total volume, i.e., the section, of the sample in which the bond breakage occurred can be calculated.

In addition to the bonds in the individual delaminated layers, it is necessary to obtain a measure of the bonds broken in obtaining the delaminated layers. A measure of these bonds is obtained by delaminating the samples on the Instron Tensile Tester at a strain rate of 0.05 in./ min. (0.127 cm./ min.) and noting the number and strength of the bonds broken over a volume equal to that affected in the above tensile test. The average bond strength, number of bonds, and the variance of the bond-strength distribution are calculated from the bond strengths measured on all the delaminated layers as well as those measured during delamination. From the area of bond breakage, the thickness of the sample, and the number of bonds which have been broken, the number of bonds per cubic centimeter can be calculated.

The operation of the present invention can be more clearly comprehended in examples which illustrated preferred practice. The following examples give such illustrations, however, without intending or suggesting any limitation to the scope of the operations described.

In the examples, the strip tensile strength of the sheet was measured in lb./in.//oz./yd. (g./cm.//g./m. according to the method of ASTM D-l682, except for the face that sample width is 0.5 inch (1.27 cm.) the distance between the jaws on the tensile machine is 5 inches (12.7 cm.) and the jaw speed is per minute. The tongue tear measurement was in accordance with ASTM D-39 except that specimens were 2 in. x 2.5 in. (5 cm. x 6.4 cm.).

FIGURE 1 is a schematic plan view of a tufting substrate in accordance with the invention. Nonwoven sheet 1, comprising randomly disposed filaments 2 has fusedwall perforations 3 along edges of the sheet. It will be understood that the perforations may appear at one or more edges of the sheet, generally as indicated in FIG- URE 1 along the length of a pair of opposite edges.

FIGURE 2 is an enlarged view of sheet 1 through a section showing the perforations 3 extending the depth or thickness of the sheet.

EXAMPLE I Initial webs prepared in accordance with embodiment one Linear polypropylene flake having a melt index of 4.5, and containing 0.2% by weight of a tan-coloring pigment is screw extruded at a maximum temperature of 290 C. and metered at 18 g./min. through a 0.25 inch (0.64 cm.) thick sand filter bed and a 2 inch (5 cm.) diameter spinneret of 30 cylindrical holes, each 0.015 inch in diameter x 0.020 inch in length (0.038 x 0.051 cm.) in size. The pack block is held at 275 C. and the spinneret temperature is adjusted to 272 C.

Directly below the spinneret, the filaments are drawn 3.8x to a high level of orientation.

The bundle of fibers is quenched in a 3 inch (7.6 cm.) orifice chimney using air flow of 700 feet/minute (210 m./min.). The top of the quench chimney abuts the bottom of the spinning pack to minimize the effect of air flow on the spinneret temperature. Below the quench chimney, the filaments are charged with a corona discharge device. A negative corona is formed from a four point source at a distance of 0.63 inch (1.6 cm. from a 1.25 inch (3.2 cm.) diameter bar rotating at 10 rpm. The threadline makes light contact with the target bar, the centerline of which is 8 inches (20 cm.) above the entrance to the forwarding jet. A negative voltage of 10 kv. (70 a.) is applied to the corona points.

The forwarding jet impels the filaments toward a traversing-table receiver to form a nonwoven web of randomly distributed fibers. Filament throughput is 18 grams/ minute.

Fiber properties are as follows:

Denier (0.87 tex) 7.8 Tensile, g.p.d. 4.6 Brk. elong., percent 72 Initial modulus, g.p.d. 43

The web formed in this manner is coherent, even without bonding. The filaments are randomly distributed. Basis weight is 3.6 oz./yd. (122 g./m. The appearance of the web is uniform and there is a low degree of filament aggregation. The fabric is bonded by the application of saturated steam at 97 p.s.i.g. (6.8 kg./cm. while the fabric is compressed between a canvas cloth and a 16-mesh wire screen. The tensile strength is 7.7 lb./in.//oz./yd. (41 g./cm.//g./m. and the tongue tear strength is 8.5 lbs.//oz./yd. "(114 g.// g./m. The filaments in the web exhibit high crystallinity and a birefringence of at least 0.016.

Ten nonwoven Webs of polypropylene filaments prepared in a similar manner are evaluated for use as pri- 11 mary rug backing materials. The webs are coded B, C, D, E, L, N, O, P, Q, and R in Table I below. A dimethyl polysiloxane lubricant is applied to each web to provide a total pickup of 1% by weight, based on the dry web.

Initial webs prepared in accordance with embodiment two A nonwoven web of 14% low-oriented and 86% highoriented isotactic polypropylene filaments is prepared as follows: polypropylene (melt flow rate 12) is spun through a 30-hole spinneret at a rate of 18 g./min. total and through a -hole spinneret at a rate of 3 g./min. total. Each spinneret hole for both spinnerets is 0.015 in. (0.038 cm.) in diameter. The temperature of the 30- hole spinneret is 242 C. and the 5-hole spinneret, 220 C. The filaments from the 30-hole spinneret are led around a heated feed roll operating with a surface temperature of 118 C., and advanced by means of an idler roll canted with respect to the heated roll. A total of 5 wraps is used on the heated feed roll, which is operated with a surface speed of 243 yd./min. (222 m./min.). The filaments leaving the heated feed roll are then passed 5 wraps around an idler roll/draw system operating cold with a surface speed of 858 yd./min. (785 m./min.). These high-oriented filaments are thus drawn 3.5x, are 7.48 denier (0.83 tex) per filament and have a tenacity of 4.03 g.p.d. The filaments from the 5-hole spinneret are led to a heated roll operating with a surface temperature of 95 C., and a surface speed of 703 yd./min. (642 m./min.). The filaments are in contact with the heated roll for 180. The filaments leaving the heated roll are then passed to a draw roll operating cold with a surface speed of 852 yd./min. (779 m./min.). The filaments are in contact with the draw roll for 180". These low-oriented filaments are thus drawn 1.21 are7.73 denier, 0.86 tex) per filament and have a tenacity of 1.62 g.p.d. The filaments from both spinnerets meet and are guided so the low-oriented filaments are uniformly dispersed throughout the high-oriented filaments. The filaments are then electrostatically charged with a corona discharge device, passed into a draw-jet and subsequently deposited on a moving belt to form a nonoven web of randomly distributed continuous filaments.

The filamentary web, unit weight 3.84 oz./yd. (130 g./m. is bonded by passing it at a speed of yd./min. (9 m./min.) while under restraint between one porous metal plate and one solid plate, each faced with cloth, for a distance of 37 in. (94 cm.) through a steam chamber in which saturated steam is maintained at a pressure of 75 p.s.i.a. (5.3 kg./cm. The restraint on the web is 0.75 lb./in. //oz./yd. (1.56 g./cm. //g./m. The bonded sheet is lubricated by immersing in a 4% aqueous dispersion of a mixture of methyl hydrogen polysiloxane and dimethyl polysiloxane which also contains 0.4% of a surface active agent (sodium alkylarylsulfonate). The sheet is then squeezed between two rolls with a nip pressure of 50 p.s.i.g. (3.5 kg./cm. at a speed of 1.5 yd./min. (1.4 m./min.) and dried in a circulating hot air oven for 45 minutes at 93 C.

The bond strength, variance and bond concentration of the bonded sheet are summarized below.

Characteristics of bonded sheet:

Average bond strength (8) 1.04 g.

Bond strength variance (r 5.35.

No. bonds/cm. S NQs 11.5 10 g./cm. Filament-breaking strength (f) 24.0 g.

N 's/ 4.79 l0 /cm.

Eight nonwoven webs prepared in a similar manner are evaluated for use as primary rug backing materials. These webs are coded A, F, G, H, I, I, K and M in Table I below.

Nine of the initial webs prepared in accordance with embodiment one and all eight of the webs prepared in accordance with embodiment two are subjected to a spark-discharge treatment to produce performations along one edge of the web, each perforation having a fused wall running the depth of the hole. The opposite edge is left untreated. The frequency of the perforations, their size, and separation from one another are shown in Table I. The number of holes per square inch is determined by actual count and represents an average count taken over 6 one-inch areas. Hole size is measured optically using a -power microscope with a calibrated eyepiece. Between about 50 and 75 holes are measured for each web and the size recorded include the minimum and maximum hole diameter and the average diameter of all holes measured. Distances between holes are measured in the same manner as the hole size. The value recorded in each instance is the shortest edgeto-edge distance between two holes.

The remaining web (sample 0) is hot-perforated by passing a plurality of heated needles through the web along one edge thereof. The opposite edge is left untreated as in the above mentioned seventeen samples. In operation, sample 0 is supported on a felt pad. A metal plate, on which are mounted fine, smooth, unbarbed, pointed needles, arranged in rows and spaced 64 to the square inch, is connected to a heating source to provide for maintenance of a temperature of about 200 C. in the needles. The temperature is sufiicient to fuse the filaments of the web in the immediate vicinity of each needle. The heated needle-plate is pressed against the web so that the needles pass completely through the web and are then instantaneously removed whereby the web is provided with 64 perforations per square inch. The size and spacing of the holes are then determined as above and are reported in Table I.

The treated nonwoven webs so obtained are then tufted with nylon carpet yarn, leaving two inches inside of each edge of the web untufted. Tufting is done using a standard commercial tufting machine with conventional needles having a diameter of 0.140-inch (0.356 cm.) operating at a spacing of 7 stitches per inch (2.8 per cm.) with tuft rows at 0.188 inch (0.48 cm.) separation. The tuft height is 0.44 inch (1.11 cm.).

Each of the tufted webs is then subjected to six wash cycles (30 minutes each) at F. using a 0.05% by weight concentration of a commercial laundry detergent. Washing is carried out in a typical household washing machine of the agitator type.

The tufted webs are then removed and examined for delamination resistance as evidenced by fuzzing. It is observed that the untreated edges of all samples are fuzzed. The treated edges of samples A through D where an average of only 10 or 16 fused-edge holes are present, are also fuzzed. All other treated edges have suflicient fuzz and delamination-resistance to permit processing in commercial rug-making operations.

The edge of each web is then tested to determine its ability to withstand the stress encountered during pintentering, as is done in commercial rug-making operations. The pin-tentering operation is simulated by attaching the web edge to pins mounted rigidly in a 6-inch (15.24 cm.) long wooden strip, the pins being spaced about 0.25 inch (0.64 cm.) apart, and then attempting to tear the web by pulling the web against the pins. The strip is of the type commercially available as carpet tackless strip. In all cases, when a fuzzed edge is so tested the fibers slide past one another and the web is pulled through the pins when subjected to stress.

The treated edges of samples A through P do not tear or rip apart and hence the selvage provided is satisfactory. The treated edges of samples Q and R wherein too many fused-edge perforations are present, fail by rupture or tearing along a given line of holes. Such failure or in-line tear is generally in the direction perpendicular to the direction of pull on the sample.

The above results are summarized in Table I below.

TABLE I Number of Arrauge- Type Smallest Average Largest Sample Holes/in. ment of of Hole Hole Hole (average) Holes 1 Sheet I Diameter, Diameter, Diameter,

mm mm. mm.

Treated edges:

A 10 L II 0. 7 1. 1. 8 L I 0. 7 1. 1 1. 7

20 L II 0. 7 1. 3 3. 1

21 L II 0. 8 1. 3 3. 2

23 L II 0. 6 1. 1 2. 0

24 L II 0. 6 1. 2 2. 2

28 R II 0. 5 1. 2 2. 3

36 R I 0. 3 O. 6 1. 1

49 L II 0. 4 0. 7 1. 2

l L=Holes arranged in square, in-line pattern: R=Holes are randomly located. 2 I=Prepared as described in embodiment I; 1I=Prepared as described in embodiment II.

Strength Smallest Average Longest Delamina- Retention Distance Distance Distance tion (Perform- Sample Between Between Between Resistance ance in Holes, Holes, Holes, (Rating Tentering mm. mm. mm. After Test After Wash Testfi Washing) Treated Edges:

A 6. 0 8. 1 10.5 F P B.-. 5. 9 7. 7 10. 7 F P C 6. 0 7. 4 10. 8 F P D 4. 3 6. 2 8. 7 F P E. 2. 3 6. 4 10. 5 P P F- 2. 6 6. 1 10. O P P G 3. 3 5. 1 7. 3 P P H- 1. 5 7. 2 16. 0 P P I 1. 6 5. 5 8. 0 P P .T 2. 0 5. 8 8. 4 P P K 1. 7 6. 3 l1. 0 P P L- 0. 2 4. 2 9. 1 P P M 2. 4 3. 6 5. 0 P P N 0.3 4. 0 8. 6 P P O. 0.3 2. 5 3. 8 P P P. 0.3 2. 7 9. 1 P P Q- 0. 6 2. 0 4. 1 P F R 0. 2 1. 5 4. 1 P F and the strength retention tests.

While the above example describes the preparation of highly desirable embodiments of the present invention, it is obvious that suitable modifications can be made without departing from the teachings set forth here.

The delamination resistance of virtually any nonwoven sheet comprised substantially of thermoplastic fibers, including staple fibers and/or continuous filaments arranged at random or in order, may be improved by hot-perforating the sheet at a multiplicity of points. Such nonwoven sheets include, for example, those produced in accordance with the teachings of Belgian patent 625,998.

While the products of this invention are particularly suited for use as carpet backing materials, they are not limited to that use. Other tufted products in which they may serve as backing material include chenille bedspreads, pile linings, upholstery materials, and imitation furs.

What is claimed is:

1. A tufted carpet having tufting yarns in stitched engagement with a primary backing which is a self-bonded nonwoven sheet of continuous, randomly disposed, linear oriented, crystalline polymeric filaments of from 3-15 denier said filaments being of polymer selected from the group consisting of isotactic polypropylene, linear polyethylene, crystalline copolymers of at least 75% propylene or ethylene with up to of other copolymerizable monomers and mixtures of isotactic polypropylene or linear polyethylene with up to 25 of other polymers,

said sheet prior to tufting having an average edge bond count of between about 30 and bonds per filaments and perforations along edges thereof to within about inch of the tufted area at a hole density between about 20 and 80 per square inch, the filaments at the walls of each perforation being fused throughout the depth of the perforation.

2. A tufted carpet in accordance with claim 1 wherein the holes along edges of the backing are between about 0.2 and 3 mm. in diameter and the distance between adjacent holes is in the range of 0.2 and 16 mm.

3. A tufted carpet in accordance with claim 2 wherein the filaments comprise polypropylene.

4. A self-bonded nonwoven sheet of continuous, randomly disposed, linear oriented, crystalline, polymeric filaments of from 3-15 denier said filaments being of polymer selected from the class consisting of isotactic polypropylene, linear polyethylene, crystalline copolymers of at least 75 propylene or ethylene with up to 25 of other copolymerizable monomers and mixtures of isotactic polypropylene or linear polyethylene with up to 25 of other polymers, said web having an average edge bond count of between about 30 and 80 bonds per 100 filaments, and as a selvage, perforations along edges thereof at a hole density between about 20 and 80 per square inch, the filaments at the walls of each perforation being fused throughout the depth of the perforation.

5. The web of claim 4 wherein the holes along edges of the web are between about 0.2 and 3 mm. in diameter 1 5 and the distance between adjacent holes is in the range of 0.2 and 16 mm.

6. The web of claim 5 wherein the filaments comprise polypropylene.

7. A bonded nonwoven sheet comprising a matrix of synthetic organic fibers being of polymer selected from the group consisting of isotactic polypropylene, linear polyethylene, crystalline copolymers of at least 75% propylene or ethylene with up to 25% of other copolymerizable monomers and mixtures of isotactic polypropylene or linear polyethylene with up to 25% of other polymers, said fibers being interconnected at a multiplicity of points throughout the sheet by bonds having a strength greater than 0.1 gram, the average strength of these bonds being at least 0.9 gram and less than the matrix fiber breaking strength, the bond strength distribution being characterized by a variance of at least 4, the number of bonds being such that the product of the number of bonds per cubic centimeter and the average bond strength is greater than 5x10 g./cm. and this product divided by the fiber breaking strength is less than 9X10 /cm. the said sheet having as a selvage, perforations along edges thereof at a hole density between about 20 and 80 per square inch, the filaments at the walls of each perforation being fused throughout the depth of the perforation.

8. The product of claim 7 wherein the fiber denier is between 3 and 15.

9. The product of claim 7 wherein the matrix fiber is isotactic polypropylene having a birefringence in the range of from 0.020 to 0.040.

10. The product of claim 9 which additionally contains polypropylene fiber having a birefringence of less than about 0.03 as a binder fiber.

11. A tufted carpet having a primary backing which prior to tufting is the sheet of claim 7.

References Cited UNITED STATES PATENTS 2,385,870 10/1945 Lashar et al. 16l-116 2,430,868 11/1947 Francis 156-583 X 2,810,950 10/1957 Rice 161-65 3,049,466 8/1962 Erlich 161252 X 3,060,072 10/1962 Parlin et al 16181 3,126,297 3/1964 Diamantopoulos 117140 JACOB H. STEINBERG, Primary Examiner.

ALEXANDER WYMAN, Examiner.

G. D. MORRIS, Assistant Examiner. 

7. A BONDED NONWOVEN SHEET COMPRISING A MATRIX OF SYNTHETIC ORGANIC FIBERS BEING OF POLYMER SELECTED FROM THE GROUP CONSISTING OF ISOTACTIC POLYPROPYLENE, LINEAR POLYETHYLENE, CRYSTALLINE COPOLYMERS OF AT LEAST 75% PROPYLENE OR ETHYLENE WITH UP TO 25% OF OTHER COPOLYMERIZABLE MONOMERS AND MIXTURES OF ISOTACTIC POLYPROPYLENE OF LINEAR POLYETHYLENE WITH UP TO 25% OF OTHER POLYMERS, SAID FIBERS BEING INTERCONNECTED AT A MULTIPLICITY OF POINTS THROUGHOUT THE SHEET BY BONDS HAVING A STRENGTH GREATER THAN 0.1 GRAM, THE AVERAGE STRENGTH OF THESE BONDS BEING AT LEAST 0.9 GRAM AND LESS THAN THE MATRIX FIBER BREAKING STRENGTH, THE BOND STRENGTH DISTRIBUTION BEING CHARACTERIZED BY A VARIANCE OF AT LEAST 4, THE NUMBER OF BONDS BEING SUCH THAT THE PRODUCT OF THE NUMBER OF BONDS PER CUBIC CENTIMETER AND THE AVERAGE BOND STRENGTH IS GREATER
 11. A TUFTED CARPET HAVING A PRIMARY BACKING WHICH PRIOR TO TUFTING IS THE SHEET OF CLAIM
 7. 